German phrase
Ich rufe um ~ Uhr zurück.
Meaning
I'll call you back at ___
When to use it
It promises a callback. It sets a clear time for returning the call.
Example dialogue
Ich habe dich eben verpasst.
I just missed you.
Ich rufe um 18:15 Uhr zurück.
I'll call you back at 18:15.